1. Field of the Invention
The present invention relates to a chip-type electronic component to be surface mounted on a conductive pattern of a circuit board or the like.
2. Discussion of Background
The miniaturization of electronic devices accomplished in recent years has inspired efforts to achieve ever smaller chip-type electronic components. For instance, dimensions have been reduced to attain currently existing chip-type laminated ceramic capacitors having a length of 0.6 mm, a width of 0.3 mm and a thickness of 0.1 to 0.3 mm.
The component of the known art as described above includes a substrate having a roughly rectangular paralellepiped shape and two external electrodes to be soldered onto a conductive pattern of a circuit board or the like. Each external electrode is provided at one of two diametrical ends in the lengthwise direction of the substrate so as to cover one surface in its lengthwise direction, two surfaces in its widthwise direction and two surfaces in its thicknesswise direction.
When mounting the chip-type electronic component of the known art onto a conductive pattern of a circuit board or the like, it is necessary to allow for insulating gaps between the sides in its widthwise direction and sides of adjacent chip-type electronic components, or between sides in its widthwise direction and sides of adjacent circuit elements, since the electrodes that partially cover the sides may cause electrical shorting.
Also, when mounting the chip-type electronic component of the known art onto a conductive pattern of a circuit board or the like by means of soldering, an adverse phenomenon occurs. The weight of the component causes the molten solder to flow from under the external electrodes in a widthwise direction toward adjacent components provided on the circuit board. As a result, it is necessary to allow for insulating gaps between the sides in its widthwise direction and sides of adjacent chip-type electronic components, or between sides in its widthwise direction and sides of adjacent circuit elements, to ensure that the excess molten solder does not cause any electrical shorting.
Thus, while super miniaturization of chip-type electronic components has been successful, the extent to which mounting density can be improved is still limited.
As a means for solving this problem, Japanese Unexamined Patent Publication No. 201634/1995 discloses a component that includes a substrate having a roughly rectangular paralellepiped shape and two external electrodes to be soldered onto a conductive pattern of a circuit board or the like. Each external electrode is provided at one of two diametrical ends in the lengthwise direction of the substrate so as to cover only the two surfaces in its thicknesswise direction.
As another means for improving the mounting density, Japanese Unexamined Patent Publication No. 156514/1990 discloses a component that includes a substrate having a roughly rectangular paralellepiped shape and two external electrodes to be soldered onto a conductive pattern of a circuit board or the like. Each external electrode is provided at one of two diametrical ends in the lengthwise direction of the substrate so as to cover only one of the two surfaces in the thicknesswise direction of the substrate.
However, since the external electrodes in both of these prior art components are formed over their entire width, the phenomenon whereby the molten solder flows from under the external electrodes in a widthwise direction toward adjacent components provided on the circuit board, cannot be prevented.
Still as another means for improving the mounting density, Japanese Unexamined Patent Publication No. 55333/1997 discloses a component that includes a substrate having a roughly rectangular paralellepiped shape and two external electrodes to be soldered onto a conductive pattern of a circuit board or the like. Each external electrode is provided at one of two diametrical ends in the lengthwise direction of the substrate so as to cover two surfaces in its widthwise direction and two surfaces in its thicknesswise direction. Since the external electrodes are provided at diametrical ends in the lengthwise direction of the component, a similar problem to that of the electronic component disclosed in the aforementioned Japanese Unexamined Patent Publications occurs.
Furthermore, chip-type electronic components are usually surface mounted by means of reflow soldering. In this process, before mounting the external electrodes, a solder paste is applied to portions of the conductive pattern of a circuit board or the like where electrodes are to be mounted, after which the chip-type electronic component is set in place by ensuring that the external electrodes are positioned on the solder paste. Next, the solder paste is molten by way of applying heat after which the external electrodes of the chip-type electronic component become soldered to the conductive pattern on the circuit board or the like.
However, when the solder paste becomes molten during the reflow soldering process, its buoyancy and the like cause the chip-type electronic component to float on the circuit board which results in misalignment of the component.
With the appearance of ever smaller chip-type electronic components in recent years, floating and misalignment of minute chip-type electronic components has become common.
In order to prevent such floating and misalignment, the chip-type electronic components of the prior art must be held at a specific position until the molten solder becomes solidified, resulting in poor efficiency in the surface mounting process.
In addition, because the external electrodes of the chip-type electronic component in the prior art are provided at diametrical ends in the lengthwise direction of the substrate, a large solder fillet forms between the external electrodes and the conductive pattern when it is surface mounted on a circuit board or the like. These solder fillets may cause shorting between the chip-type electronic component and adjacent chip-type electronic components or between the chip-type electronic component and the conductive pattern of a circuit board or the like.
In order to prevent this problem from occurring, the mounting density at which chip-type electronic components are mounted must be reduced and, as a result, it presents an obstacle to achieve an improvement in the mounting density.
Yet as another means for improving the mounting density, Japanese Unexamined Patent Publication No. 55084/1993 discloses a laminated ceramic capacitor that includes a substrate having a roughly rectangular paralellepiped shape, internal electrodes and two external electrodes to be soldered onto a conductive pattern of a circuit board or the like. Portions of internal electrode films lead out to one surface in the thicknesswise direction of the substrate and external electrodes are provided where the portions of the internal electrodes are led out, to electrically connect the lead-out portions to the external electrodes. The ceramic substrate is achieved by alternately laminating internal electrode films and dielectric layers.
However, since the external electrodes in this prior art are flat, it is impossible to prevent floating and misalignment during the soldering process, resulting in shorting due to the presence of solder fillets.
It is an object of the present invention to provide a chip-type electronic component that achieves outstanding mass productivity.
It is a further object of the present invention to provide a chip-type electronic component that can be mounted onto a conductive pattern of a circuit board or the like by means of soldering.
It is a still further object of the present invention to provide a chip-type electronic component that can significantly improve the mounting density of a circuit board.
It is a still further object of the present invention to provide a chip-type electronic component that can be soldered with a high degree of reliability while reducing the likelihood of misalignment when it is surface mounted on a circuit board or the like.
In order to achieve the objects described above, the present invention discloses a chip-type electronic component in two modes. The chip-type electronic component in the first mode includes a ceramic substrate, at least one internal electrode film and a plurality of external electrodes. The ceramic substrate has two side surfaces in its lengthwise direction and two side surfaces in its widthwise direction intersecting each other, and is further provided with at least one flat surface in its thicknesswise direction.
The internal electrode film is embedded in the ceramic substrate. The surface of the internal electrode film lies roughly parallel to the flat surface of the ceramic substrate.
Each of the external electrodes is provided on the flat surface of the ceramic substrate at diametrical ends in the lengthwise direction of the ceramic substrate. They are each electrically continuous with the internal electrode film and are each formed over distances from the two side surfaces in the widthwise direction of the ceramic substrate.
As explained above, the two side surfaces in the lengthwise direction of the ceramic substrate and the two side surfaces in the widthwise direction of the ceramic substrate intersect. In other words, the ceramic substrate is formed in a roughly rectangular parallelepiped shape. This shape makes it possible to adopt a manufacturing method in which individual chip-type electronic components are manufactured by means of, for instance, cutting a wafer provided with a large number of chip-type electronic components, in a grid pattern. Thus, a chip-type electronic component achieving outstanding mass productivity is achieved.
Since the internal electrode film is embedded in the ceramic substrate and the external electrodes are each electrically continuous with the internal electrode film , electrical characteristics of the ceramic substrate and the internal electrode film can be extracted through the external electrodes. Also, since the internal electrode film is embedded in the ceramic substrate, the ceramic substrate renders a protective effect with respect to the internal electrode film.
By adopting the structure in which the external electrodes are provided at diametrical ends in the lengthwise direction of the ceramic substrate, a chip-type electronic component that can be mounted on a circuit board by means of soldering the external electrodes onto a conductive pattern of a circuit board or the like, is realized.
Since the flat surface in the thicknesswise direction of the ceramic substrate is provided with external electrodes, this flat surface can be soldered to the conductive pattern of a circuit board or the like. Thus, the quantity of solder flowing from under the external electrodes of the component, in directions that are toward adjacent components provided on the circuit board, can be minimized, thereby improving the mounting density at the circuit board. Also, since the surface of the internal electrode film extends almost parallel to the flat surface of the ceramic substrate in its thicknesswise direction, when the electronic component is mounted on a circuit board or the like, the internal electrode film is made to lie almost parallel to the mounting surface of the circuit board.
Furthermore, as a critical feature, by adopting the structure in which the side surfaces in the lengthwise direction of the substrate and the side surfaces in the widthwise direction of the ceramic substrate intersect each other, and the external electrodes are each formed over distances from the two side surfaces in the widthwise direction of the ceramic substrate, areas of the flat surface that cannot be soldered are formed between the external electrodes and the two side surfaces in the widthwise direction of the ceramic substrate.
Consequently, when mounting the chip-type electronic component on a circuit board, there is no room for solder fillets and the like to be formed between the external electrodes of the chip-type electronic component and an adjacent circuit element even if the distance between the chip-type electronic component and an adjacent chip-type electronic component or the distance between the chip-type electronic component and a circuit element is reduced. Thus, the mounting density on the circuit board is a greatly improved.
The chip-type electronic component in the second mode includes a ceramic substrate, at least one internal electrode film and a plurality of external electrodes. The ceramic substrate has two side surfaces in its lengthwise direction and two side surfaces in its widthwise direction that intersect each other, and is further provided with at least one flat surface in its thicknesswise direction.
The internal electrode film is embedded in the ceramic substrate. The surface of the internal electrode film intersects the flat surface of the ceramic substrate almost orthogonally and a lead-out portion is exposed to the outside of the ceramic substrate at the flat surface. The external electrodes are constituted of the lead-out portions exposed at the flat surface.
The chip-type electronic component according to the second mode described above achieves advantages similar to those achieved by the chip-type electronic component according to the first mode. The two side surfaces in the lengthwise direction of the ceramic substrate and the two side surfaces in the widthwise direction of the ceramic substrate intersect. In other words, the ceramic substrate is formed in a roughly rectangular parallelepiped shape. This shape makes it possible to adopt a manufacturing method in which individual chip-type electronic components are manufactured by means of, for instance, cutting a wafer being formed with a large number of chip-type electronic components, in a grid pattern. Thus, a chip-type electronic component achieving outstanding mass productivity can be achieved.
The internal electrode film is embedded in the ceramic substrate, with the surface of the internal electrode film extending almost perpendicular to the flat surface constituting one of the surfaces of the ceramic substrate in its thicknesswise direction and the lead-out portions exposed at the flat surface. Since the external electrodes are constituted of the lead-out portions exposed at the flat surface, the electrical characteristics of the ceramic substrate and the internal electrode film can be extracted through the external electrodes. Also, since the internal electrode film is embedded in the ceramic substrate, the ceramic substrate renders a protective effect with respect to the internal electrode film.
By adopting the structure in which the external electrodes constituted of the lead-out portions of the internal electrode film are provided at diametrical ends in the lengthwise direction of the ceramic substrate, a chip-type electronic component that can be mounted on a circuit board by means of soldering the external electrodes onto a conductive pattern of a circuit board or the like is achieved.
Since the external electrodes are constituted of the lead-out portions of the internal electrode film, they can be soldered onto the conductive pattern of the circuit board or the like, at the flat surface constituting one surface of the ceramic substrate in its thicknesswise direction. Thus, the quantity of solder flowing from under the external electrodes in the lengthwise direction of the ceramic substrate is restricted, thereby improving the mounting density at the circuit board.
By adopting the structure in which the external electrodes are each constituted of the lead-out portions of the internal electrode film and are each formed over distances from the two side surfaces in the widthwise direction of the ceramic substrate, areas of the flat surface that cannot be soldered are formed between the external electrodes and the two side surfaces in the widthwise direction of the ceramic substrate. Consequently, when mounting the chip-type electronic component on a circuit board, there is no room for solder fillets and the like to be formed between the external electrodes of the chip-type electronic component and an adjacent circuit element even if the distance between the chip-type electronic component and an adjacent chip-type component or the distance between the chip-type electronic component and a circuit element is reduced. Thus, a great improvement in the mounting density on the circuit board is achieved.
In addition, the internal electrode film is provided so that its surface extends almost perpendicular to the flat surface constituting one surface of the ceramic substrate in its thicknesswise direction, with the lead-out portions exposed to the outside of the ceramic substrate at the flat surface. The external electrodes are constituted of the lead-out portions exposed at the flat surface. With this structure, the lead-out portions, can be soldered as a means for surface mounting. The film thickness of the external electrodes constituted of the lead-out portions, which are part of the internal electrode films, is extremely small. Thus, the quantity of solder adhered to the external electrodes is extremely small so that the force applied by the molten solder to the chip-type electronic component is greatly reduced compared to that at external electrodes in the prior art. Consequently, the chip-type electronic component according to the present invention is soldered onto a circuit board with a high degree of reliability without causing floating, misalignment and the like. After the solder solidifies, the lead-out portion of the internal electrode film is connected to the conductive pattern on the circuit board or the like via the solder.
Furthermore, since no floating, misalignment or the like occurs when the chip-type electronic component is soldered to the circuit board, steps such as holding the chip-type electronic component at a specific position until the molten solder solidifies and the like are not required, thereby achieving an improvement in the efficiency with which surface mounting is implemented at a circuit board or the like.
Moreover, the film thickness of the external electrodes which are constituted of the lead-out portions that are part of the internal electrode film is extremely small. As a result, the quantity of solder adhered to the external electrodes becomes very small to greatly reduce the solder fillets formed between the external electrodes and the conductive pattern of a circuit board or the like compared to that at external electrodes in the prior art. Thus, the surface mounting density is improved.
The chip-type electronic component according to the present invention may be any of various types of chip-type electronic components such as capacitors, inductors, resistors, thermistors, varistors and the like. It may also be a combined component achieved by combining these chip-type electronic components. The material constituting the ceramic substrate and the electrical characteristics of the ceramic substrate, the type of circuit elements to be employed and the like should be selected in correspondence to the desired type of chip-type electronic component to be achieved.
For instance, the ceramic substrate should be constituted of dielectric ceramic to obtain a ceramic capacitor. In this case, by alternately laminating internal electrode films and dielectric layers, a laminated ceramic capacitor is achieved.
When obtaining an inductor, the ceramic substrate should be constituted of a magnetic substance such as ferrite with a conductor provided at the ceramic substrate. The conductor should be provided at a surface of the ceramic substrate or at the inside of the ceramic substrate, in a linear, spiral or zigzag form.
Appropriate ceramic substrate materials and circuit elements should be selected to achieve specific desired characteristics when producing other chip-type electronic components such as resistors, thermistors and varistors.